1. Field of the Invention
The present invention relates to an optical information processing apparatus in which an optical recording medium is scanned by a focused light beam and information is recorded thereon and/or reproduced therefrom.
2. Related Background Art
Hitherto, various kinds of media, such as the disk type, card type, tape type, and the like have been known as forms of recording media to record information thereon, and to read out the recorded information therefrom, by using light beams. Among them, the demand for an optical information recording medium formed in a card shape (hereinafter, referred to as an "optical card") is increasing more and more as a small-sized and light-weight portable medium having a large memory capacity.
FIG. 1 is a schematic plan view of such an optical card 101. Reference numeral 102 denotes an information recording area; 103 indicates an information track; reference numerals 104 and 104' denote track selecting areas; and reference numeral 105 indicates a home position of a light spot.
Information is recorded as an optically detectable recording bit train (information tracks) on the optical card 101 by scanning by a light beam modulated in accordance with recording information and focused to a micro spot. In this case, to accurately record information without causing any difficulty such as crossing of information tracks or the like, the irradiating position of the light spot needs to be controlled (auto tracking; hereinafter, referred to as an "AT") on the optical card surface in a direction perpendicular to the scanning direction. On the other hand, in order to irradiate the light spot as a micro spot of a stable size irrespective of any bending or mechanical error of an optical card, it is necessary to control auto focusing (hereinafter, referred to as an "AF") in the direction perpendicular to the optical card surface. In addition, the AT and AF are also necessary in the reproducing mode.
FIG. 2 shows a constructional diagram of an apparatus for recording information onto and reproducing information from an optical card. Reference numeral 106 denotes a motor to drive the optical card 101 in the directions indicated in the diagram by the double-head arrow 107 is a light source such as a semiconductor laser; 108 a collimating lens to convert the light from the light source 107 into the parallel light beam; 109 a beam splitter; 110 an objective lens; 111 a tracking coil; 112 a focusing coil; 113 and 114 condenser lenses; 115 and 116 photoelectric converting elements for tracking signal detection and for focusing signal detection; 117 a tracking controlling circuit; and 118 a focusing controlling circuit. The coils 111 and 112 are combined with magnets (not shown) and construct a tracking actuator and a focusing actuator, respectively. Currents are allowed to flow through the tracking coil 111 and focusing coil 112 in response to commands from the control circuits 117 and 118 on the basis of a tracking signal and a focusing signal which are detected by the photoelectric converting elements 115 and 116, respectively, so that the objective lens 110 is moved and the AT and AF are executed. On the other hand, reference numeral 119 denotes a system controller to control a recording and reproducing apparatus and 120 indicates a group of various control signals which are output from the system controller 119. Although signals other than signals 120 are also output from the controller 119, they are not shown here. Reference numeral 121 denotes an optical head and 122 indicates a drive motor to move the optical head in the direction indicated by arrow u in FIG. 1.
The light beam from the light source 107 is converted to the parallel light by the collimating lens 108 and is transmitted through the beam splitter 109. Thereafter, the light is focused onto the recording track on the optical card 101 by the objective lens 110. The light reflected by the recording track is again transmitted through the beam splitter 109 and is divided into two light beams by a beam splitter 109'. The divided light beams are respectively focused onto the photoelectric converting element 115 for tracking signal detection and the photoelectric converting element 116 for focusing signal detection by the condenser lenses 113 and 114. Electric signals from the photoelectric converting elements 115 and 116 are used as a tracking error signal and a focusing error signal by the tracking controlling circuit 117 and the focusing controlling circuit 118, respectively. By allowing currents to flow through the tracking coil 111 and focusing coil 112, the objective lens 110 is moved and the AT and AF are executed.
FIG. 3 is a detailed diagram of the tracking controlling circuit 117.
In the diagram, the same parts and components as those in FIG. 2 are designated by the same reference numerals. A tracking error signal 203 detected by the photoelectric converting element 115 is transmitted through a phase compensating circuit 202 and a limiter 301 and is amplified by an operational amplifier 302 and is input to the tracking coil 111. The limiter 301 is used to limit the maximum current which flows through the coil 111. The maximum current is limited a to prevent a breakage of the actuators due to the inflow of an overcurrent or to prevent unnecessary motion of the objective lens when noises appear in the signal 203 due to dust or scratches on the medium.
However, in the foregoing conventional apparatus, even in the case when a variation in sensitivity of the actuators occurs, depending on the type of apparatuses used, the maximum current is constant. Therefore, the moving distance of the objective lens due to the limited current differs, dependent on each of the actuators. That is, in the case of the actuator having a high sensitivity, the moving distance of the objective lens is large. On the contrary, in the case of the actuator of a low sensitivity, the moving distance is small. Therefore, large noises appear in the signal 203 due to dust or scratches on the medium. A variation in movement amount of the objective lens occurs when the current is limited depending on the type of apparatus used. This presents a problem such that in a certain apparatus, the AT is effective notwithstanding the existence of a large amount of dust, but in another apparatus, the AT is made ineffective, even by the existence of a small amount of dust, and in this manner, the quality of the apparatus becomes unstable.